Wasp Numbers in Honeydew Beech Forest

Honeydew on a filament

Vespula wasps are most abundant in beech forests of the South Island, which are naturally infested with endemic scale insects that produce ‘honeydew’ (Beggs 2001).

Honeydew is produced by a native scale insect (similar to an aphid). The insect inserts its mouth-parts into the trunk of the beech tree to feed on the trees sap. The excess sap passes through the gut of the scale insect and forms a sugary droplet at the end of the insect. Wasps collect these droplets for food.

Wasps are able to carry loads of about 15 microlitres of honeydew at a time.

The honeydew-producing scale insects provide an energy-rich food resource for Vespula wasps. Wasps reduce the standing crop of honeydew by more than 90% for 5 months of the year and so compete with native species and honeybees that also consume honeydew (Beggs 2001).

Densities of wasps in these forests are typically 8–34 nests/ha (average 12/ha; Barlow et al. 2002). At their peak, there is an average biomass of 3.8 kg of wasps/ha (10 000 worker wasps/ha), which is greater than the combined biomass of birds and exotic rodents/mustelids (Thomas et al. 1990).

Wasps can affect nutrient cycling in the honeydew beech forest community by reducing the flow of carbon to micro-organisms in the phyllosphere and the soil, ultimately this could affect soil solution chemistry.